So in the end, I was able to resolve this by using a different OS image. The original FROM andrejreznik/python-gdal:stable image that I was using was a Debian-based image, but I didn't realize that the OS I was upgrading to, andrejreznik/python-gdal:py3.11.10-gdal3.6.2, is an Ubuntu image. On a whim, I experimented with andrejreznik/python-gdal:py3.10.0-gdal3.2.3 which is a Debian image, and this actually worked - when deployed to AWS, gunicorn could be run with no problem.

Although I was able to fix the problem, I must admit that I still don't really understand why this happened, and I would like to know how to resolve it. Why is it that switching from Debian to Ubuntu locally had no problems, but as soon as the Ubuntu image went to AWS, it could no longer find gunicorn?